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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

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  1. J

    Astigmatism as an Aberration in Optics

    There is often confusion between astigmatism of the eye and astigmatism as an aberration in an optical instrument, so I thought I would attempt an explanation. It has even been suggested that one could cancel out the other but this is not the case. I stand open to correction for the following...
  2. J

    Zeiss Lens Wipes

    These will be familiar to many but as questions about lens cleaning crop up frequently, I thought it worth a mention. I came across them at my local drug store and they were no more expensive than the usual household items. Zeiss state that they contain no perfumes and that there are only two...
  3. J

    The Price of Fluorite (Calcium fluoride)

    I recently received a catalogue from Edmund Optics in which they are offering plano-convex fluorite lenses (uncoated) in diameters ranging from 12,5 mm to 50 mm for scientific applications. They have a surface quality of 40-20 scratch/dig. The 50 mm lenses cost €375 (or €300 for >6 pcs.), so...
  4. J

    Focus Overtravel (compatibility for the near-sighted)

    A recent discussion on another thread prompted me to try and measure the amount of focus overtravel in dioptres in various bins. This is the amount by which the focus wheel turns beyond the infinity setting for the normally-sighted or those wearing glasses. If the focus overtravel is limited...
  5. J

    Birding binoculars on a tripod

    A tripod is indispensable if one wishes to measure the AFOV of a bin or assess its resolution with a booster, but sometimes it can be of use for birding with moderate magnifications. Prerequisites are a tripod adapter (I use the Leica adapter, which works well with all roof prism bins) and that...
  6. J

    Do Leica use Dielectric Coatings?

    I'm inclined to doubt it. When Leica upgraded the Ultravids to Ultravid HDs they claimed improved transmission and everyone assumed that they had adopted dielectric prism coatings. However, in their catalogue they only mention P40 phase coating and "HighLux System." The latter is described as...
  7. J

    Better than Gitzo?

    Some five years ago I bought a Series 2 Gitzo basalt tripod, a GT2942L. There were then fewer alternatives and the choice was determined by the requirement for light weight, but also height for my 192 cm and the 65 mm straight Diascope I was then using. Basalt was a compromise, 200 g heavier...
  8. J

    Measurement of Effective Aperture

    Occasionaly binoculars don't meet their published specifications. If I recall correctly the original versions of the Canon 10x42 IS had an effective aperture of 37 mm and then there was a 12x50 Optolyth, which was more like a 12x40. I recently stumbled across a test by Henry Link of the Zen-Ray...
  9. J

    Dielectric and Phase Coatings - do they interrelate?

    There was a recent discussion here:- http://www.birdforum.net/showthread.php?t=251175 on phase and mirror coatings, which prompted me to go back and investigate some of my bins. One can check for phase coating by viewing a white TFT screen through the objective (i.e. backwards) and rotating a...
  10. J

    User report, Kowa Genesis 8x33

    I recently purchased a Kowa Genesis (Prominar XD) 8x33. My desire was for premium performance, but as a no. 3 binocular in addition to a 7x42 and 10x42 I could not really justify the higher costs of the Europran premium competitors. The intended use was for travel, when also carrying scope and...
  11. J

    The Relationship of Eye Relief to Eye Lens Diameter and FOV

    I wear glasses so adequate eye relief is critical for me, particularly as the converging lenses for my far-sightedness effectively reduce the eye relief, whereas diverging lenses for the near-sighted would effectively lengthen it. I was looking at 8x32s recently at my dealer's and he insisted...
  12. J

    Internal Focussing Lenses, Positive or Negative?

    There are still a few roof prism binoculars available with bridge focussing (e.g. the Zeiss 8x56 Dialyt and the Optolyth Royal models) but the now minor advantage of two fewer air/glass surfaces is probably outweighed by the superior ruggedness and close focus capability of internal focussing...
  13. J

    Tripod stability: a few thoughts and some primitive experiments.

    I'll start off with a few controversial assertions and am open to contradiction: 1) There are no substitutes for leg diameter and weight. 2) The fewer the number of leg sections, the better. 3) Soft surfaces damp better than hard. 4) For a given tripod height it really doesn't matter if you...
  14. J

    Pipedreams anyone?

    Despite the wide variety of binocular configurations on the market there are some formats such as 7x30, which are sorely missed by many. The marketing people are probably not going to listen to us but it would be interesting to hear the wishes of other BF members, technically feasible of...
  15. J

    How to quantify AFOV without the complete specs.

    Often manufacturers' specifications omit the apparent field of view and the advertising blurb would try to suggest for instance, that a 6,5 bin with a FOV of 140 m @ 1000 m could be classified as wide angle. This is definitely not the case. Sometimes the true field of view in degrees is quoted...
  16. J

    SV purchase and a bit of gossip

    Over the past few months I have had several opportunities to look through the Swarovski EL 10x42 SV and had become a little dissatisfied with my 10x42 FL. With its enormous 26 mm eye lenses it has excellent eye relief for glasses wearers and an ease of view that one would suspect 5 mm or 6 mm...
  17. J

    Test of eleven 8x32 binoculars

    Holger Merlitz has just published the following test. Although many of his reports are in English, this one is unfortunately only in German. However, one could try Google translate and I would attempt to clarify if there are any ambiguities. http://www.holgermerlitz.de/8x32/test8x32.html...
  18. J

    Swarovski Astro Adapter II

    Yesterday it was announced on this dealer's forum, http://www.juelich-bonn.com/ that the long awaited Swarovski astro adapter is now available. I drove down to Bonn today and collected one. It closely resembles the original adapter with two flat sides so that one does not have to tighten it via...
  19. J

    New 30-60x WA and 20-70x Zooms for Meopta 82 mm Apo Scope

    http://www.meopta.com/en/new-meostar-s2-spotting-scope-1404043227.html Unusual that, according to the specs, the AFOV would appear to decrease slightly with increasing magnification. John
  20. J

    New Model, BD 7x28 IF

    http://www.minox.de/index.php?id=4790&L=1 Obviously of limited interest to birders and I would have thought it would have been easy to accommodate a minimum IPD of less than 58 mm. RRP in Germany is €279. John
  21. J

    Astigmatism and exit pupil

    I followed a recent dicussion on the binoculars forum on contact lenses and there were some interesting contributions from looksharp65, who is an optometrist. I should be grateful if he or anyone else could answer the following questions. Firstly:- Assuming the eye does not need correction for...
  22. J

    Belebach 552, the best lightweight video head?

    The above may be an unqualified statement as I have little experience with video heads. Some years ago I got into the rut of using a ballhead with my scope. This was an attempt to save weight on an old Gitzo Series 4 tripod I had aquired in the '80s for use with a view camera. Its 3-way head...
  23. J

    Swarovision Test

    The "Vögel" (German birding magazine) test of top of the line 10x42s has been updated with measurements for the Swarovision EL. I have posted a brief summary in the main binocular forum. John
  24. J

    Test of six small refractors

    The German magazine, "Interstellarum" recently published a test of six small astronomical refractors and I thought this might be of interest to BF readers. Astronomical telescopes have several disadvantages for birding. None is waterproof, they are often heavier than comparable spotting scopes...
  25. J

    Vortex 2x Booster

    There was a recent thread here on boosters and, encouraged by some measurements made by Steve (Mooreorless), I went and purchased a Vortex Doubler. I had taken my 10x42 FLs (good fit) and 7x42 SLCs (less good) with me to the dealer and when I got home was impatient to try out the Doubler on my...
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